Alkenyl complexes of platinum group metals: a platform for diverse reactivity patterns

Intermediates for many catalysis reactions reported in the literature are metal‐alkyl and metal‐alkenyl, including metallacycloalkane species. Synthesis and reactions of metal‐alkyl, alkenyl and metallacyle complexes have shown a great deal of development during the past few decades. This review summarizes the significant contributions reported on metal‐alkenyl compounds, specifically those containing at least a carbon chain with pendant alkene group [M―CH₂CH₂CH?CH₂]. Although metal‐alkenyl complexes are stable with strong chelating diphosphines and with a decrease in the ligand donor strength, the complexes can decompose without any ambiguity. For example, platinum‐dialkenyl complexes react readily via β‐hydrogen elimination and reductive elimination promoted by the nature of the ligand, solvent and length of carbon chains. These complexes can also undergo intramolecular irreversible isomerization and this leads to the selective catalytic isomerization of 1‐alkenes to 2‐alkenes in the presence of platinum‐dialkenyl complexes as catalysts. Perhaps the most striking manifestations of flexibility are the facile and complete intramolecular and intermolecular alkene metathesis to yield the corresponding metallacycloalkenes in the presence of Grubbs’ catalysts. The diverse chemical reactivity of these complexes demonstrates both the scope and complexity of metal‐alkenyl chemistry depending on the nature of ligand and metal. Copyright © 2014 John Wiley & Sons, Ltd.